1. Field of the Invention
The invention relates generally to physical vapor deposition (PVD) of metal films.
The invention relates more specifically to DC magnetron sputtering of ferromagnetic metals such as nickel (Ni) onto semiconductor substrates and the like for forming metallization such as found in the electrically-conductive interconnect layers of modern integrated circuits.
2a. Cross Reference to Related Patents
The following U.S. patent(s) is/are assigned to the assignee of the present application, and its/their disclosures is/are incorporated herein by reference:
(A) U.S. Pat. No. 5,242,566 issued Sep. 7, 1993 to N. Parker; PA1 (B) U.S. Pat. No. 5,320,728 issued Jun. 14, 1994 to A. Tepman; and PA1 (C) U.S. Pat. No. 5,540,821 issued Jul. 30, 1996 to A. Tepman. PA1 (a)Y. M. Ahn et al (Samsung Electronics, Korea), STUDY ON MAGNETO-OPTICAL TbFeCo THIN FILMS MAGNETRON-SPUTTERED FROM TARGETS WITH LOW AND HIGH PERMEABILITIES, Intermag 97 conference of April 1997; and PA1 (b) Y. Nakamura et al (Japan Energy Corp.), INFLUENCE OF PERMEABILITY ON Co TARGET USAGE, pp. 651-656, Proc. of 4.sup.th ISSP (Kanazawa, Japan 1997), Jun. 4-6, 1997.
2b. Cross Reference to Related Other Publications
The following publication(s) is/are cited here for purposes of reference:
3. Description of the Related Art
The electrically-conductive interconnect layers of modern integrated circuits (IC) are generally of very fine pitch (e.g., 10 microns or less) and high density (e.g., hundreds of lines per square millimeter).
If there is nonuniformity of thickness or nonhomogeneity in other attributes of the precursor metal films that ultimately form the metallic interconnect layers of an IC, such lack of uniformity can lead to out-of-tolerance topographies and improper semiconductor fabrication. The latter can be detrimental to the operational integrity of the ultimately-formed IC. As such it is desirable to form metal films with good uniformity across each of mass-produced wafers.
The metal films of integrated circuits may be formed by physical vapor deposition (PVD). One low cost approach uses a DC magnetron sputtering apparatus such as the Endura.TM. system available from Applied Materials Inc. of California for sputtering metals onto semiconductor wafers or other like workpieces.
Aluminum (Al) is the most common metal that is deposited by DC magnetron PVD sputtering. Aluminum can be characterized as a polycrystalline, electrically conductive material whose crystals have a face-centered cubic (FCC) structure. One of the characteristics of Al is that it is an essentially nonmagnetic material. (Al may be considered paramagnetic though.)
Recently it has been proposed that magnetic metals such as nickel (Ni) may also be deposited using the Endura.TM. or like DC magnetron PVD systems.
Because nickel (Ni) is a ferromagnetic material, it presents new problems that had not been earlier posed by nonmagnetic materials such as aluminum. In particular, magnetic flux fields generated within the DC magnetron PVD system may be significantly altered due to shunting or short circuiting of the magnetic flux through the magnetically conductive material of ferromagnetic (e.g., Ni) targets. Such shunting can make it difficult to strike a plasma or sustain a generally-uniform plasma over time and can lead to associated problems such as nonuniform deposition. There is a question as to whether ferromagnetic targets of practical thicknesses (e.g., 3 millimeters or greater) can be used for sputtering with a DC magnetron PVD system.
The present inventors have through experimentation, isolated a number of physical attributes of ferromagnetic targets (e.g., nickel targets) that collectively correlate with how uniform the deposited film is across the substrate and how efficiently the material of the target is used. These collective correlations are disclosed herein together with designs for improved ferromagnetic targets.